An engine of a vehicle generates torque for generating cruising power, and for driving a generator and an auxiliary device such as a compressor for an air conditioner.
In an example of a first control, an engine in an idling operation generally performs feedback control to maintain the idling speed at a constant speed. In this idling operation of the first control, a target rotation speed in the idling operation is set in accordance with an ON/OFF signal of a compressor.
According to an example of a second control published in each of JP-A-2003-269216 and JP-A-2004-68664, a controller increases the idling speed of an engine to boost electric power generated using an electric generator when the controller detects low voltage or decrease in remaining capacity of a battery due to shortage in generating performance of the electric generator.
In the first control, the idling speed is controlled by operating only an intermittent ON/OFF signal of a controlled device, i.e., the auxiliary device. Therefore, in this first control, the idling speed is controlled irrespective of states of uncontrolled devices such as the engine, the generator, and other devices. Consequently, controllability is not necessarily excellent. For example, drive torque of the generator and other devices may act oppositely to the operation of the intermittent ON/OFF signals of the controlled device in the idling operation. In the first control, adverse effects due to the opposite acts are not taken into consideration, consequently the idling speed may be wastefully operated. In addition, the engine speed may not be quickly increased from the idling rotation.
In the second control, the controller may not instruct to increase engine speed until the controller detects lowering in battery charged level. Accordingly, shortage in engine speed may be continued, and such continuous shortage exerts an adverse influence to the battery life. In consideration of this adverse influence, the engine speed may be changed in response to a small change in battery charged level. However, in this case, control response may become excessively quick, consequently the control may cause hunting.
In each of the first and second control systems has a relatively simple structure. For example, the engine speed is changed in accordance with input parameters such as intermission of the auxiliary device and the state of battery charging. In these simple structures, effect produced by the controls may be limitative.